New observations of climate-relevant properties of atmospheric aerosols in Namibia, southern Africa.

Southern Africa, and in particular its western part, Namibia, is considered a climate change hotspot by the IPCC and is at risk of severe temperature-related changes. As examples, models projections suggest by the end of the century: 1) Increase of surface temperature of +4 to +7°C; 2) destruction of the stratocumulus cloud deck along the western coast; and 3) decrease of the fog inland. The role of aerosols in this context is still not completely quantified, due to their high spatial and temporal variability, the many sources responsible for the complex mixture and the lack of continuous observations. Most of the past regional climate modelling (RCM) and intensive field campaigns focussed primarily on constraining the radiative effects of the seasonal biomass burning aerosols generally occurring in the end of the austral winter (August to October). However, the aerosol spectral optical properties, aerosol optical depth and the organic fractions are not studied enough to provide a firm understanding of regional aerosol load, interaction with radiation and interplays in relation to particle chemistry.

In this work, we present the first analysis of new long-term ground-based aerosol observations conducted since april 2022 at Gobabeb Namib Research Institue (23°33’40‘’S, 15°02’24’’E) in Namibia. Gobabeb is located in the hyperarid Namib desert and it is under the influence of different air masses, transporting maritime and biomass burning aerosols, amongst others. The measurements of optical and physical properties of the aerosol mixtures are analysed to provide with the aerosol single scattering albedo and mass absorption, scattering and extinction efficiencies which are needed to evaluate the first Africa-based Earth system model by the Global Change Institute at the University of Witwatersrand in South Africa. The in situ surface data are complemented by the analysis of pre-existing observations such as those from the AERONET sunphotometers.